A high-affinity,low-capacity receptor for estradiol in normal and anemic mouse spleen cytosols

A high-affinity, low-capacity receptor activity for 17 β-estradiol has been identified in cytosols of mouse spleen, normal or erythropoietic. It appears to be a protein which sediments at 5S in high-salt gradients and with a peak at 4S and a shoulder at 8-10S in low-salt gradients. In addition to 17 β-estradiol, only 17 α-estradiol and 5(10)-estren-3 α, 17 β-diol competed successfully with the steroid ligand. A K_d of 1.5 × 10^?9 M and 4.1 fmoles/mg protein for the number of binding sites were calculated for the receptor activity of early erythropoietic spleen cytosols.